Prosthesis anchoring and deploying device

ABSTRACT

A system for intraluminally delivering and deploying stents and other prostheses includes an outer catheter, an inner catheter movable axially relative to the outer catheter, and an anchoring device mounted to a distal end region of the inner catheter. The anchoring device includes one or more control features that interact with a linking structure proximally disposed on the prosthesis, preferably including one or more loops. The control features and loops interact by surface engagement to anchor the prosthesis relative to the inner catheter in a nonfrictional manner, thus to maintain lower axial prosthesis deployment and retraction forces. In one version of the anchor, the control features extend radially outward from a sleeve. In another version, the control features are formed in respective recesses which also receive the loops or other linking structure.

BACKGROUND OF THE INVENTION

The present invention relates to systems for intraluminally deliveringand deploying self-expanding stents and other prostheses, and moreparticularly to such systems that incorporate mechanisms for retrievingpartially deployed prostheses.

Stents, stent-grafts, and other body implantable tubular devices areemployed in a wide variety of applications to maintain the patency ofbody lumens and guide the flow of blood and other body fluids throughthe lumens. These devices are employed in vascular applications, e.g. inpulmonary and thoracic vessels, and in arteries such as the coronary,renal, carotid, and iliac arteries. In addition to these vascularapplications, the devices are used in the esophagus, duodenum, biliaryduct, and colon. These devices may be either radially self-expanding orballoon-expandable in character. When deployed within body lumens,self-expanding devices radially expand into contact with surroundingtissue, typically assuming a diameter less than a fully expanded orrelaxed state diameter. Consequently, an internal elastic restoringforce acts outwardly against the tissue to assist in fixation of thedevice. Self-expanding devices frequently are preferred, due to thisself-fixation capability.

Most applications employing radially self-expanding devices requireintraluminal delivery of the device in a configuration suitable fordelivery, i.e. radially compressed to a reduced-radius state against itsinternal elastic restoring force. To this end, prosthesis deliverysystems frequently include two catheters: an outer catheter releasablycontaining the radially compressed prosthesis in a lumen near its distalend, and an inner catheter contained in the lumen, positioned against orotherwise engaged with the prosthesis. The prosthesis is deployed bymoving the outer catheter proximally while holding the inner catheter inplace. This effectively moves the inner catheter and the prosthesisdistally relative to the outer catheter, allowing the prosthesis toradially self-expand as it emerges from the distal end of the outercatheter.

In either event, there arises on occasion a need to reverse thedeployment. The need may arise from the physician's desire to repositionthe prosthesis along the intended treatment site. Once a substantialportion of the prosthesis is free of the outer catheter, it may be movedin the proximal direction. However, at this point it is virtuallyimpossible to move the prosthesis in the distal direction withoutretracting it proximally, back into the outer catheter. Accuratepositioning of the prosthesis during deployment is challenging, in thatit usually requires fluoroscopic imaging, and the difficulty isincreased by the tendency of the many self-expanding devices to axiallyshorten as they radially self-expand. The need to retract a prosthesiscan arise from other factors, e.g. a realization during deployment thata prosthesis of a different axial length or radius would be moreeffective at the designated treatment site.

In many conventional deployment and delivery systems, retraction of apartially deployed prosthesis is virtually impossible. To provide aretractable prosthesis, an inner catheter or other member can besurrounded by a high friction sleeve or gripping member as shown in U.S.Pat. No. 5,026,377 (Burton et al.), with the portion of an innercatheter supporting the sleeve and surrounded by the prosthesis. Whenthe outer catheter radially compresses the prosthesis, it simultaneouslypresses the prosthesis into a frictional engagement with the sleeve.Accordingly, when the outer catheter is moved relative to the innercatheter, the prosthesis tends to remain with the inner catheter ratherthan following the outer catheter. A similar approach is shown in U.S.Pat. No. 5,817,102 (Johnson et al.) in which an exterior catheterradially compresses a stent into contact with a restraining sleeve thatsurrounds an interior catheter.

While these arrangements permit proximal retraction of a partiallydeployed stent or other prosthesis, they rely on a frictional engagementof the prosthesis with the inner member, through the gripping member orrestraining sleeve. The force due to the frictional engagement must besufficient to overcome the tendency of the prosthesis to move with theouter catheter as the outer catheter moves relative to the inner member.This frictional force acts in the axial direction, but requires a forceacting in the radial direction to urge the prosthesis against thegripping member. The required radial force adds to the radial forcealready exerted by the prosthesis against the outer catheter due to itsinternal elastic restoring force, thus to increase the axial pushingforce required to overcome friction between the prosthesis and outercatheter, and deploy the prosthesis.

Another factor inherent in this approach is the reduction in thefrictional holding force as prosthesis deployment progresses, largelydue to the diminishing portion of the prosthesis length subject to thefrictional hold. As deployment progresses, the prosthesis becomesincreasingly easy to deploy. Conversely, when the prosthesis is beingpulled back into the catheter to reconstrain it, the reconstrainmentforce increases as more and more of the prosthesis is pulled into thecatheter. This tendency can be counteracted by increasing the frictionalholding force, but this in turn increases the radial force required toovercome the frictional hold, once again increasing the force requiredfor ordinary deployment.

Other arrangements involve axially tight or locking engagements ofprostheses with inner member coupling structures. Examples of thesearrangements are seen in U.S. Pat. No. 6,350,278 (Lenker et al.) andU.S. Pat. No. 5,733,325 (Robinson et al.). These systems permitprosthesis retraction, but impose unduly stringent tolerances upon thecoupling structure. Further, they require close attention and care onthe part of the physician or other user when loading a prosthesis intothe system, to ensure that the required coupling is achieved.

Therefore, the present invention is disclosed in terms of severalembodiments, each directed to at least one of the following objects:

-   -   to provide a prosthesis deployment system with the capability of        retracting partially deployed prostheses, without any        substantial increase in the axial forces required to deploy the        prostheses;    -   to provide a prosthesis deployment system that permits        retracting of the prosthesis at a later stage in its deployment,        in terms of the fraction of the prosthesis axial length exposed,        without degrading or losing retraction capability;    -   to provide a deployment device that has greater stent retention        capability if the need arises for withdrawing a partially        deployed stent;    -   to provide a deployment device capable of retracting partially        deployed device in which an open-frame support structure is        covered, e.g. as in stent-grafts; and    -   to provide a prosthesis anchoring device suitable for attachment        to an inner catheter or other inner member of a conventional        prosthesis delivery and deployment system to provide the        capability of retracting partially deployed prostheses.

SUMMARY OF THE INVENTION

To achieve these and other objects, there is provided a device foreffecting an intraluminal delivery and controlled deployment of a bodyimplantable prosthesis. The device includes an elongate prosthesisdelivery member having a distal wall segment adapted to contain aradially self-expanding prosthesis in a reduced-radius delivery stateagainst an internal restoring force. A radially self-expandingprosthesis is contained in the distal wall segment and therebymaintained in the reduced-radius delivery state. The prosthesis includesa linking structure near a proximal end of the prosthesis. An elongateprosthesis control member is mounted for axial travel relative to thedelivery member, toward and away from a delivery position in which adistal end region of the control member extends along the distal wallsegment of the delivery member and is disposed radially inwardly of theprosthesis. A control feature is disposed along the distal end region ofthe control member and extends radially outwardly from the controlmember beyond a radial midpoint of the linking structure when in thedelivery position with the prosthesis so contained. Thus, the controlfeature is positioned to allow limited distal travel of the deliverymember and prosthesis relative to the control member, and to effect asubstantially non-frictional surface engagement with the linkingstructure upon said limited distal travel, to anchor the prosthesisagainst further distal travel relative to the control member.

The delivery member can comprise an outer catheter with a lumen runningsubstantially along its complete length. The control member can comprisean elongate inner catheter disposed in the outer catheter lumen.Preferably a proximal region of the inner catheter extends beyond aproximal end of the outer catheter, to facilitate the use of the innercatheter proximal end to control the position of the inner catheterdistal region relative to the outer catheter. This facilitates controlof the prosthesis deployment from outside the body.

If desired, the control member can be provided with several controlfeatures, equally angularly spaced apart from each other about thecontrol member, for use with a prosthesis in which the linking structureincludes angularly spaced apart loops or other linking members. Aone-to-one correspondence of control features and loops is workable, butnot required. In one embodiment, three control features are used inconjunction with six loops formed at a proximal end of the prosthesis.

In a preferred embodiment, a tubular sleeve supports a symmetricalarrangement of control features, and is sized to facilitate itsslideable installation onto the distal end region of the control member.The sleeve and control features are formed as a unitary member,preferably more rigid than the control member to provide more positivecontrol over the prosthesis through engagement of the control featureswith the loops or other linking members. The control features can besurrounded by substantially closed loops of a prosthesis linkingstructure, in which case the features can control both proximal anddistal prosthesis movement.

One aspect of the present invention is that the control feature outerends define a control feature diameter less end than an inside diameterof the delivery member distal wall segment. At the same time, the radialspacing in between the control features and distal wall segment is lessthan half of a radial thickness dimension of the prosthesis linkingstructure. Consequently, the control member and control features areslideable relative to the delivery member with no frictional drag.

Yet, the control feature outer ends are sufficiently close to the distalwall section to prevent the linking structure or another part of theprosthesis from wedging into the space between the control features anddistal wall segment.

A salient feature of the present invention is that the control member isoperable to move the prosthesis proximally relative to the deliverydevice—or alternatively, to maintain the prosthesis substantiallystationary while the delivery device is moved distally relative to thecontrol member—through a surface engagement of each control feature withthe prosthesis linking structure. The control features apply axialforces to the linking structure. Unlike the frictional prosthesisretraction systems discussed above, there is no need for frictionalcontrol of the prosthesis, and accordingly, no need for the additiveradial force that undesirably increases the axial force required todeploy the prosthesis. Further, because the axial forces in the presentsystem do not depend on friction, they do not diminish as prosthesisdeployment progresses. As a result, the prosthesis can be fullyretracted from a stage close to complete deployment, e.g. with up toninety-five percent of its length positioned distally of the deliverydevice.

Another aspect of the present invention is a prosthesis delivery anddeployment device. The device includes an elongate prosthesis deliverymember having a distal wall segment adapted to contain a radiallyself-expanding prosthesis in a reduced-radius delivery state against aninternal restoring force. An elongate control member is mounted foraxial travel relative to the delivery member, toward and away from adelivery position in which a distal end region of the control memberextends along the distal wall segment of the delivery member. Aprosthesis anchor is mounted to the distal end region and comprises atleast one elongate axially directed control feature extending radiallyoutwardly from the control member. The control feature thereby ispositioned to effect a releasable engagement with a proximal-end linkingstructure of a radially self-expanding prosthesis when in the deliveryposition and with the prosthesis so contained. The anchor, when in saidengagement with the linking structure, is operable to anchor theprosthesis against distal travel relative to the control member.

Preferably, the anchor comprises a plurality of the elongate axiallydirected control features positioned to engage the linking structure.Then, the linking structure preferably includes a plurality of elongateaxially directed loops, each associated with a different one of thecontrol features. The anchor further can include a cylindrical anchoringbody with a centrally located axial opening adapted to receive thecontrol member and facilitate and mounting of the anchor in surroundingrelation to the control member. The anchor advantageously can be morerigid than the control member, to provide a more positive engagementwith its associated loop.

In one preferred version, the anchoring body has a recess directedinwardly from an outside surface of the anchoring body and adapted toreceive a loop or other proximal-end linking structure of theprosthesis. The associated control feature is disposed in the recess, tobe surrounded by the loop when the loop is received into the recess. Inthis version, the depth of the recess exceeds the radial thickness ofthe loop, so that the complete loop may be radially inwardly disposedrelative to the outside surface.

A further aspect of the present invention is a prosthesis anchoringdevice adapted for fixation to a prosthesis deployment member. Thedevice includes a generally cylindrical anchoring sleeve having acentral opening extending axially therethrough to facilitate a slideableinstallation of the anchoring sleeve onto an elongate prosthesisdeployment member for fixation along a distal end region of thedeployment member. A control feature extends radially outwardly from theanchoring sleeve and is adapted to extend radially into a proximal-endlinking structure of a radially self-expanding prosthesis when theprosthesis is maintained in a reduced-radius state against an internalrestoring force and selectively axially aligned with the distal endregion. The control feature, with the anchoring sleeve fixed to adeployment member and when so extending into a proximal-end linkingstructure of a radially self-expanding prosthesis so maintained andaligned, is adapted to engage the linking structure to prevent anysubstantial distal movement of the prosthesis relative to the deploymentmember.

Preferably, the control feature is elongate, directed axially, andadapted to extend into a prosthesis proximal-end linking structuretaking the form of an elongate, axially extended loop. When surroundedby the loop, the control feature prevents any substantial distalmovement of the loop relative to the anchoring body. In a more preferredversion of the device, a plurality of the elongate control features areangularly spaced apart from one another about the anchoring body.

In another version of this device, the anchoring body includes a recessreceding radially inwardly from its outside surface to receive thelinking structure. The control feature is disposed within the recess.Typically, the depth of the recess exceeds the thickness of the linkingstructure. In systems that employ an outer catheter or other deliverydevice with a distal wall section designed to maintain a radiallyself-expandable prosthesis in a reduced-radius delivery state, theanchoring body can be dimensioned for a close fit within the distal wallsection. As a result, the distal wall segment cooperates with the wallsof the recess to capture the linking structure within the recess, whilepermitting the anchoring body to slide axially along the distal wallsection.

To provide a more secure retention of the linking structure, the recesscan be formed with a size and shape corresponding to that of the linkingstructure. For example, if the linking structure comprises an elongatelinking strand formed into a loop, the recess can have a perimeter thatclosely corresponds to a perimeter of the loop. The control featuredisposed in the recess is surrounded by the loop when the loop isretained in the recess. When surrounded by the loop, the control featureprevents any substantial distal movement of the loop relative to theanchoring body. As a result, the deployment member is operable throughthe anchoring body to deploy and retract the prosthesis.

In short, an anchoring body formed according to the present invention,with a central aperture sized according to a conventional prosthesisdeployment catheter and with one or more control features sizedaccording to the corresponding loops or other linking structure of aselected prosthesis, can considerably improve the prosthesis retractioncapability of a prosthesis delivery and deployment system, withoutincreasing the axial force required for deployment.

Several additional features enhance deployment system performance,regardless of whether the control features are recessed. For example,when the anchoring device is provided as a unitary structure including acylindrical anchoring body and outwardly protruding control features,the device may be attached to a conventional inner catheter or othercontrol member, fixed to the inner catheter at a location selected inaccordance with the compressed length of the prosthesis to be deployed.Further, a relatively hard anchoring device can be fixed to a softer,more compliant inner catheter or control member, providing the capacityto negotiate serpentine internal passageways, while at the same timeproviding more positive control over the prosthesis through therelatively rigid control features.

Another useful feature arises from the provision of elongate controlfeatures and their axial orientation along the control member. Thisaligns the major dimension of each control feature with the direction ofthe forces applied through the control feature to the prosthesis, toovercome its tendency to follow the outer catheter or other prosthesisdelivery member. As a result, the control features are more stable andless prone to unwanted flexure. The elongate axially directed features,as compared to pins or other features with circular cross sections, arebetter suited to limit twisting of the prosthesis relative to thecontrol member. At the same time, the control features can havetransverse widths selected to allow limited prosthesis rotation.

Yet another advantage arises from the positioning of each controlfeature to allow limited distal travel of the delivery member andprosthesis before the prosthesis engages the linking structure, and thento effect non-frictional surface engagement with the linking structureresponsive to the limited distal travel. As compared to previousdeployment systems with interlocks designed to prevent any axialmovement of a prosthesis relative to an inner catheter or other controlmember, the novel coupling of the control feature and linking structurecan be manufactured under tolerances that are less stringent. Further,loading the prosthesis into an outer catheter or other delivery member,while maintaining a prosthesis radially compressed and coupled to thecontrol member through the control features, is much easier.

Yet another aspect of the present invention is a process for loading aradially self-expanding prosthesis for subsequent deployment in a bodylumen, comprising the following steps:

-   -   a. positioning a radially self-expanding prosthesis along and in        surrounding relation to a distal end region of an elongate        prosthesis control member with a proximal end linking structure        of the prosthesis disposed near axially spaced apart first and        second features that extend radially outwardly from the control        member;    -   b. with the prosthesis so positioned, radially contracting the        prosthesis to a reduced-radius delivery state against an        internal elastic restoring force, to move the linking structure        into a delivery position between the first and second features,        whereby the first and second features cooperate to limit axial        travel of the prosthesis relative to the control member to a        predetermined range so long as the prosthesis remains in the        delivery state; and    -   c. selecting an axial dimension of the linking structure with        respect to an axial spacing between the first and second        features whereby the predetermined range is at least twice the        axial dimension of the linking structure.

Thus in accordance with the present invention, systems forintraluminally deploying radially self-expanding stents, stent-graftsand other implantable devices may be used to retract and withdraw suchdevices, even when deployment is near completion. There is no need forfrictional retention of the device, and no resulting increase in axialforce required for deployment. With the devices nearly deployed, yetretractable, physicians can evaluate prosthesis length, radius,placement relative to the treatment site, and other factors with morecertainty as a basis for making critical decisions.

IN THE DRAWINGS

For a further understanding of the above and other features andadvantages, reference is made to the following detailed description andto the drawings, in which:

FIG. 1 is a partial side elevation of a stent delivery and deploymentsystem constructed in accordance with the present invention;

FIG. 2 is a side elevation of a radially self-expanding stent deployablewith the system of FIG. 1;

FIG. 3 is a forward elevation of a stent anchoring device employed inthe system of FIG. 1;

FIG. 4 is a perspective view of the anchoring device;

FIG. 5 is a sectional view taken along the line 5-5 in FIG. 1;

FIG. 6 is a schematic top view of a control feature of the anchoringdevice, surrounded by a loop of the stent;

FIG. 7 is a schematic side view, partially in section, of the controlfeature and loop;

FIGS. 8-11 schematically illustrate use of the system to deploy thestent;

FIG. 12 is a schematic view similar to that in FIG. 7, showing analternative embodiment anchoring device;

FIG. 13 is a schematic view illustrating another alternative embodimentanchoring device;

FIG. 14 is a partial side elevation of an alternative embodiment stentdelivery and deployment system constructed according to the presentinvention;

FIG. 15 is a forward elevation of a stent anchoring device employed inthe system of FIG. 14;

FIG. 16 is a perspective view of the anchoring device;

FIG. 17 is a top view illustrating a loop of a radially self-expandingstent disposed in a recess of the anchoring device;

FIG. 18 is a forward elevation, partly in section, of the loop in therecess;

FIG. 19 is a forward elevation of an alternative embodiment stentanchoring device; and

FIG. 20 is a top view illustrating another alternative embodimentanchoring device and stent linking member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, there is shown in FIG. 1 a system 16 forintraluminally delivering and deploying a radially self-expanding stent,stent-graft, or other prosthesis. System 16 includes an elongate andpliable outer catheter 18 constructed of a biocompatible material suchas polypropylene, FEP, HDPE, PTFE, or PET. A central lumen 20 runs thelength of catheter 18. The tubular wall of catheter 18 includes a distalwall segment 22 containing a radially self-expanding stent 24. Withreference to FIG. 2, stent 24 preferably is of open weave or meshconstruction formed of multiple helically wound and braided filaments orstrands 26 of a flexible material such as body compatible stainlesssteel. Other suitable materials include shape memory alloys such asNitinol, or biocompatible polymers. Other filament configurations may beemployed, including non-braided and non-helical configurations. Stent 24is shown in a free or relaxed state, i.e. the state assumed by the stentwhen subject to no external force. Returning to FIG. 1, catheter 18radially compresses stent 24, acting against an internal elasticrestoring force of the stent to maintain the stent in an axiallyelongated, reduced-radius delivery state.

An elongate and pliable inner member or catheter 28 extends along alength of the outer catheter, contained in lumen 20. When system 16 isconfigured for stent delivery as shown in FIG. 1, a distal region 30 ofinner catheter 28 is surrounded by the stent. Inner catheter 28 ismovable axially relative to outer catheter 18. A proximal region 32 ofthe inner catheter extends proximally beyond a proximal end 34 of outercatheter 18, and is operable to control the axial position of distalregion 30 relative to distal wall segment 22 of the outer catheter.Inner catheter 28 has an axially extending lumen 36 to accommodate aguidewire 38.

An anchoring device 40 is fixed in surrounding relation to innercatheter 28, near a proximal end of distal region 32. As is laterexplained, device 40 is operable to anchor stent 24 with respect toinner catheter 28, enabling use of the inner catheter to retract andrecover a partially deployed stent.

A thrust member 42 is fixed in surrounding relation to inner catheter28, proximally spaced apart from anchoring device 40. Inner catheter 28is movable distally relative to outer catheter 18 to position thrustmember 42 against the proximal end of stent 24, whereupon further distaltravel of the inner catheter moves the stent distally relative to theouter catheter.

Inner catheter 28 is movable proximally relative to outer catheter 18 tobring anchoring device 40 into a surface engagement with stent 24.Alternatively, the inner catheter is movable distally to bring thrustmember 42 into to surface contact with the stent. Thus, the innercatheter acts as a control member, to selectively control the positionof stent 24 relative to the outer catheter.

As seen in FIG. 2, stent 24 has a proximal end 44 at which strands 26are formed into a plurality of elongate loops 46. At a distal end 48 ofthe stent, the strands are formed into a plurality of bends 50. In thisversion, twenty-four helical windings, twelve in each of two oppositedirections, form twelve of the distal end bends 50, and six proximal endloops 46. Loops 46 are equally angularly spaced apart about the stentperiphery or circumference, in increments of sixty degrees from eachloop to each adjacent loop. The optimal numbers of strands, loops andbends can differ, depending on the strand material and the procedureinvolved. The oppositely directed strands form multiple intersections orcrossing points 52. The stent is shown in its relaxed state, whensubject to no external stress.

Stent 24 is radially compressible, against an internal elastic restoringforce, to an axially-elongated, reduced-radius delivery state. As seenin FIG. 1, distal wall segment 22 of the outer catheter provides theexternal force necessary to maintain stent 24 in the reduced-radiusstate, thus to facilitate the intraluminal delivery of the stent to theintended treatment site. When contained in this fashion, stent 24 exertsa radially outward force against distal wall segment 22 as a counter tothe external force. This creates a frictional engagement of the stentand outer catheter, whereby the stent tends to follow proximal anddistal movements of the outer catheter. Stent 24 is deployed throughproximal movement of catheter 18 relative to inner catheter 28, with theinner catheter applying an axial (distal) force against the stentsufficient to overcome friction between the stent and outer catheter.This prevents the stent from moving proximally with the outer catheter.When free of outer catheter 18, stent 24 radially self-expands towardthe relaxed state shown in FIG. 2.

In system 16, stent 24 closely surrounds but is not necessarily incontact with inner catheter 28. In contrast, in deployment systems thatprovide retraction through a frictional hold on the stent or otherprosthesis, such contact not only is present, but must be maintained byexerting a radially inward force urging a stent against an innercatheter (or a sleeve or other gripping member along the innercatheter), to create a frictional hold that exceeds the frictional holdbetween the stent and the outer catheter. Thus, frictional systemsprovide for stent retraction, but at a cost: namely, a considerableincrease in the axial force delivered by the inner catheter to deploythe stent. This is because the axial force must overcome not only thefriction from the aforementioned restoring force of the stent, but theadditional friction due to the additional radial force needed to pressthe stent against the inner catheter or gripping member. System 16, byproviding an essentially non-frictional engagement of stent 24 withinner catheter 28, provides for stent retraction without increasing theaxial force needed to deploy the stent.

As seen in FIG. 1, when stent 24 is radially compressed in the deliverystate, it is releasably coupled to inner catheter 28 through anchoringdevice 40. With reference to FIG. 3, anchoring device 40 is symmetricalabout a longitudinal axis. A central opening 54 extends through thedevice, and has a diameter slightly larger than the outside diameter ofinner catheter 28 at least along the distal region. This provides aslideable fit, to facilitate installation of the anchoring device ontothe inner catheter, where the device can be fixed at its intendedlocation by an adhesive, thermal processing, ultrasonic welding or othersuitable approach. Anchoring device 40 includes a longitudinallyextending sleeve 56. Three splines or fins 58 extend longitudinallyalong sleeve 56 and radially outward from the sleeve, to respectiveradially outward ends 60.

Anchoring device 40 preferably is a unitary member, formed of a polymersuch as ABS, polycarbonate, or nylon 12. Thus, it can be harder or morerigid than inner catheter 28 and outer catheter 18. As a result, theanchoring device when engaged with stent 24 through loops 46 can morepositively anchor and otherwise control the position of the stent.

The nature of the coupling between anchoring device 40 and stent 24 isbest understood with reference to FIGS. 5-7. As best seen in FIG. 5,each of fins 58 extends through one of loops 46, to a point beyond itsassociated loop and just inside of distal wall segment 22. Preferably,an outer diameter defined by outward ends 60 is less than the insidediameter of the distal wall segment by an amount less than the radialthickness of loops 46, i.e. the diameter of strands 26. The result isthat in a coaxial arrangement, the radial spacing between each end 60and the distal wall segment is less than one-half the strand diameter.This arrangement ensures a positive retention of each loop about itsassociated fin.

In a satisfactory but less preferred arrangement, each fin extendsradially to position its outer end beyond a radial midpoint of itsassociated loop, i.e. beyond the geometric center of strand 26 asindicated by the broken line at 62.

In FIG. 5, loops 46 are shown spaced apart inwardly from the distal wallsegment. This is partly for convenience in illustrating the positionalrelationship between each fin and its associated loop. Further, at leasta portion of each loop is spaced apart from the distal wall segment, byvirtue of the fact that the profile of each loop as viewed in FIG. 5extends as a chord in relation to the circular profile of wall segment22. Finally, this figure illustrates that there need not be a one-to-onecorrespondence of fins to loops, although it is preferable to have asymmetrical arrangement in which the number of loops is an integralmultiple of the number of fins, as shown.

FIGS. 6 and 7 illustrate one of loops 46 surrounding its associated fin58. As shown in FIG. 6, fin 58 has a transverse width less than thecorresponding interior width of loop 46. Alternatively, fin 58 can betapered, with a width that increases in the radially inward direction,so that the loop tends to engage the opposite sides of the fin as it isplaced onto the fin. In either event, fin 58 is positioned for limitedaxial travel within the associated loop. When outer catheter 18 is moveddistally relative to inner catheter 28, loop 46 follows the outercatheter and moves distally (to the left as viewed in FIGS. 6 and 7)until a proximal end surface 64 of the fin engages a proximal insidesurface 66 of loop 46. The remaining two fins similarly engage proximalinside surfaces of their associated loops. Once the loops and fins areengaged, device 40 functions as an anchor that prevents further distalmovement of stent 24, despite further distal travel of the outercatheter. The proximal end surfaces of fins 58 extend radially, so thattogether they occupy a plane perpendicular to the axial direction. Thispromotes the anchoring function, particularly when the strand formingloop 46 has a circular profile or cross section.

It is preferred to couple fin 58 and loop 46 as shown, to allow limitedrelative axial travel. As an alternative, the fin and loop could beconfigured to form a close or tight coupling that would virtuallyprevent relative axial movement of the stent and inner catheter. Thelooser, more flexible coupling has several advantages. The loops andfins can be formed under less demanding tolerances. Further, with themore flexible coupling it is much easier for the physician to load stent24 into outer catheter 18 while maintaining the stent position relativeto inner catheter 28.

As perhaps best seen in FIG. 6, loops 46 and fins 58 are elongate in theaxial direction. Thus, the major dimension of the fin coincides with thedirection of forces applied to the loop through the fin. Further, fin 58cooperates with the opposite axially extending sides of loop 46 toprovide a more stable coupling of the loop and fin that not only limitsrelative axial travel, but also resists twisting of the stent relativeto the inner catheter, even when allowing limited relative rotation toprovide the advantages of less stringent tolerances and ease of stentloading.

Preferably a distance D between end surface 64 of the fin and an endsurface 68 of the thrust member is selected in conjunction with adiameter d of strand 26 forming the loop, to determine a range of axialtravel of stent 24 relative to inner catheter 28. In exemplaryembodiments, distance D is from 1 mm to 2 mm and diameter d is 0.3 mm.The resulting range of axial travel is 0.7 mm to 1.7 mm, or in terms ofthe ratio D/d, is from 3.3 to 6.7. Advantageously, the ratio D/d is atleast about 2.

Further, an axial length L₁ of the interior of loop 46 exceeds an axiallength L₂ of fin 58 sufficiently to permit the required freedom of axialmovement of the fin within the loop. For example, L₁ can be 5.5 mm, withL₂ being 3-4 mm. To allow limited rotation or transverse movement of theprosthesis relative to the inner catheter, an internal transverse widthW₁ of loop 46 exceeds a transverse width W₂ of the fin. Morespecifically, W₁ can be 1.5 mm and W₂ can be 0.3 mm. Advantageously, W₁is at least about twice W₂.

The use of anchoring device 40 to control stent deployment isillustrated in FIGS. 8-11. In FIG. 8, stent 24 surrounds the distalregion of inner catheter 28, radially compressed in the reduced-radiusdelivery state by outer catheter 18. Typically, stent 24 is loaded intothis position first by placing the stent in its relaxed state around thedistal end region of the inner catheter, with loops 46 axially alignedwith anchoring device 40. Then stent 24, at least along its proximal endnear the loops, is elongated axially and radially reduced sufficientlyto bring three of the loops about the three fins. The inner catheter andstent are moved proximally into the outer catheter, until the distalwall segment completely surrounds the stent, as shown in FIG. 8. At thispoint, system 16 is inserted into the body and moved distally along avessel or other body lumen, until the distal ends of the catheters arepositioned near the intended treatment site. The catheters are moveddistally over a previously positioned guidewire, not shown.

At this stage, the user controls the proximal ends of the catheters,holding inner catheter 28 substantially stationary while proximallywithdrawing outer catheter 18. Thrust member 42 engages stent 24 toprevent further proximal movement of the stent, in effect moving thestent distally relative to the outer catheter. As the stent emerges fromthe distal end of the outer catheter, it radially self-expands towardits relaxed state, as seen in FIG. 9. The arrow indicates proximalmovement of the outer catheter.

As depicted in FIG. 10, outer catheter 18 is moved proximally asufficient distance to nearly complete the deployment of stent 24. Overat least about half of its length, the stent has radially expanded intocontact with surrounding tissue (not shown) at the treatment site. Thearrow indicates that at this stage, outer catheter 18 may be moved ineither axial direction, depending on the physician's determination offactors critical to the implantation procedure; e.g. whether the stentis properly positioned, and whether the stent has a diameter and axiallength appropriate for the procedure. In practice, stent 24 may remainretractable with up to ninety-five percent of its length disposeddistally of outer catheter 18.

If the stent is properly positioned, and the earlier determinations asto stent size are confirmed, outer catheter 18 is moved further in theproximal direction, to completely release stent 24 for full radialexpansion into contact with surrounding tissue, as indicated in FIG. 11.At this point, catheters 18 and 28 are withdrawn.

Conversely, if stent 24 needs to be repositioned or replaced, outercatheter 18 is moved distally to recompress and recapture the stent,restoring the configuration shown in FIG. 8. Then, catheters 18 and 28are moved in concert to reposition the stent, or are withdrawn to allowsubstitution of another stent.

Several advantages of system 16, as compared to retraction devices thatrely on friction, can be appreciated in conjunction with FIGS. 8-11. Thefirst of these is lower axial deployment force. Anchoring device 40,unlike friction-based devices, adds nothing to the axial force needed tomaintain inner catheter 28 and stent 24 in place while proximallywithdrawing outer catheter 18. Likewise, this approach adds nothing tothe axial force needed to retract a partially deployed stent.

Moreover, the coupling of stent 24 to inner catheter 28 through theanchoring device provides substantially the same anchoring force,regardless of the extent of stent deployment. Unlike friction-basedsystems, the amount of axial holding force available to retract thestent does not diminish as deployment progresses. Thus, the physiciancan deploy stent 24 to a point of near completion as indicated in FIG.10, confident that anchoring device 40 remains capable of retracting thestent if necessary. More accurate determinations relating to stentplacement and size can be made with stent 24 at a stage close to fullstage deployment as in FIG. 10. As compared to the partial deploymentstage indicated in FIG. 9, or conventional designs that allow onlypartial deployment, the configuration in FIG. 10 provides a better basisfor making critical decisions regarding stent size and placement.

FIG. 12 illustrates part of an alternate embodiment anchoring device 70including a sleeve 72 and a plurality of pins extended radially awayfrom the sleeve, one of which is shown at 74. When stent 24 isconstrained to the reduced-radius state, pin 74 extends through one ofloops 46 or an opening in the stent lattice structure in the same manneras fin 58, while permitting a wider latitude of axial movement of theloop relative to the anchoring device. This approach may be moresuitable to a prosthesis that has less columnar strength.

FIG. 13 shows a portion of another alternative anchoring device 76 inwhich several fins, one of which is shown at 78, extend radially awayfrom a sleeve 80. A proximal end surface 82 of the fin is concave in theproximal direction. Consequently, when stent 24 is moved distallyrelative to the anchoring device, fins 78 function as hooks to morepositively capture their associated loops. The capturing function can beachieved through other profiles in end surface 82, e.g. profiles withnotches, slots, and other suitable depressions or concavities. As afurther alternative, end surface 82 can be inclined proximally as itextends radially outward to capture the associated loop.

FIG. 14 illustrates a distal portion of an alternative embodimentprosthesis delivery and deployment system 84, including an outercatheter 86, an inner catheter 88 contained in a lumen 90 of the outercatheter for axial travel relative to the outer catheter, and a radiallyself-expanding stent 92 contained in a reduced-radius state along adistal wall segment of the outer catheter. A cylindrical anchoringdevice 94 is secured to the inner catheter, and is releasably engagedwith a loop 96 at the proximal end of stent 92. In lieu of a thrustmember (e.g. 42), catheter 88 is formed with a shoulder 93 to providethe thrust member or feature.

As seen in FIGS. 15 and 16, anchoring device 94 includes a cylindricalbody 96, with an opening 98 extending axially through the body tofacilitate installation and mounting of the anchoring device along adistal end region of inner catheter 88. Anchoring device 94 is shaped toprovide a control feature, specifically a medial feature 100, thatinteracts with a loop 102 of stent 92 in much the same manner as fin 58interacts with loop 46. However, body 96 further is shaped to provide arecess 104 directed radially inwardly from an annular outside surface106 of the body. Medial feature 100 extends radially outwardly from aninside central portion of the recess, in effect forming axially directedgrooves or recess segments 108 and 110 between feature 100 and sidefeatures 112 and 114, respectively.

FIGS. 17 and 18 illustrate loop 102 retained releasably within therecess. A strand 116 forming the loop includes spaced apart longitudinalsections 118 and 120, retained respectively in grooves 108 and 110. Theoutside diameter of body 96 is less than an inside diameter of catheter86 along the distal wall segment, to enable the anchoring member toslide relative to the outer catheter. Also, the difference between thebody diameter and the inside diameter of the distal wall segment is lessthan the diameter of strand 116, to ensure that loop 102 is positivelyretained in recess 104, so long as the proximal portion of theprosthesis near loop 102 remains radially compressed.

FIG. 19 illustrates an alternative embodiment anchoring member 122, withrecesses 124 and medial features 126 formed along opposite sides of acylindrical body 128. Device 122 can be used with the single-loop stentshown in FIG. 14, or with a stent having two opposed proximal end loops.Thus, the number of recess/medial feature combinations can exceed thenumber of loops, but must at least equal the number of loops toaccommodate all loops, due to the close spacing between body 128 and theouter catheter.

In anchoring device 94, medial feature 100 and loop 102 form a couplingthat is asymmetrical, in the sense that the axial force does not actthrough a central axis of the anchoring device. Nonetheless, the narrowspacing between outside surface 106 and the inside surface of outercatheter 86 facilitates a smooth sliding movement of inner catheter 88within the outer catheter. In contrast, anchoring member 122 provides asymmetrical arrangement with a more balanced application of axialforces. In either arrangement, the number of recesses can be equal to,or an integral multiple of, the number of loops.

An advantage of anchoring devices 94 and 122, as compared to anchoringdevices without recesses, is that they can more easily accommodatecovered devices such as stent-grafts. This is because medial features100 and 126 do not extend beyond the outer surfaces of their respectiveanchoring bodies, and thus do not interfere with a graft or othercovering surrounding the stent.

FIG. 20 illustrates another alternative embodiment anchoring device 130with a cylindrical anchoring body 132 and a recess 134 directed radiallyinwardly from an annular outside surface 136 of the body. A filament orstrand 138 of a stent (not fully shown) is shaped into a loop or otherlinking member 140 at the proximal end of the stent. Recess 134 has ashape corresponding to the profile of loop 140, with a radially orientedrecess wall that substantially surrounds the loop. The recess wallfunctions as the control feature, Consequently, so long as the stent ismaintained in a reduced-radius state, anchoring device 130, throughsurface engagement with loop 140, can anchor the stent alternativelyagainst proximal and distal movement relative to anchoring device 130and its associated inner catheter.

While loop 140 provides a convenient proximal end linking member of astent, it is apparent from FIG. 20 that a bend, twist, or otherenlargement formed in strand 138 can provide a suitable surfaceengagement with body 132 when captured within recess 134. Further,strand 138 may include adjacent portions twisted together, yetterminating in a loop similar to loop 140. Looped ends are generallyfavored, due to their atraumatic character. As with previousembodiments, the stent linking structure can consist of a single loop orother linking member, or a plurality of linking loops or membersarranged angularly about the stent.

Thus in accordance with the present invention, stents and otherprostheses of the radially self-expanding type are deployable atrelatively low levels of axial force, and further are retrievable atmultiple stages of deployment. Inner catheters or other inner membersare provided with anchoring devices that have radially extending fins,recesses, or other features designed to interact with loops or otherproximal-end linking members of prostheses, to anchor the prosthesesthrough surface-to-surface engagement rather than friction, thus toprovide more positive anchoring without the need for any additionalaxial force for prosthesis deployment or retraction.

1. A device for effecting an intraluminal delivery and controlleddeployment of a body implantable prosthesis, including: an elongateprosthesis delivery member having a distal wall segment adapted tocontain a radially self-expanding prosthesis in a reduced-radiusdelivery state against an internal restoring force; a radiallyself-expanding prosthesis contained in the distal wall segment andthereby maintained in the reduced-radius delivery state, said prosthesisincluding a linking structure near a proximal end of the prosthesis; anelongate prosthesis control member mounted for axial travel relative tothe delivery member, toward and away from a delivery position in which adistal end region of the control member extends along the distal wallsegment of the delivery member and is disposed radially inwardly of theprosthesis; a control feature disposed along the distal end region ofthe control member and extending radially outwardly from the controlmember beyond a radial midpoint of the linking structure when in thedelivery position with the prosthesis so contained, thereby beingpositioned to allow limited distal travel of the delivery member andprosthesis relative to the control member, and to effect a substantiallynon-frictional surface engagement with the linking structure upon saiddistal travel, to anchor the prosthesis against further distal travelrelative to the control member.
 2. The device of claim 1 wherein: thedistal end region is surrounded by the prosthesis when in said deliveryposition.
 3. The device of claim 1 wherein: the delivery membercomprises an elongate outer catheter having a lumen runningsubstantially the entire length of the outer catheter.
 4. The device ofclaim 3 wherein: the control member comprises an elongate inner catheterdisposed in said lumen, wherein a proximal region of the inner catheterextends proximally beyond a proximal end of the outer catheter tofacilitate use of the proximal region to control a position of thedistal region relative to the outer catheter.
 5. The device of claim 1wherein: the control feature comprises a plurality of control featuresangularly spaced apart from one another about the control member distalregion.
 6. The device of claim 5 wherein: said control features haveproximal end surfaces aligned in a plane substantially normal to theaxial direction.
 7. The device of claim 5 wherein: a proximal endsurface of each of the control features is aligned with respect to thecontrol member to define an angle, relative to the axial direction,other than 90 degrees.
 8. The device of claim 5 wherein: each of thecontrol features has a proximal end surface including a concavity in theproximal direction.
 9. The device of claim 5 further including: a sleevesupporting said control features and mounted in surrounding relation tothe control member along the distal end region.
 10. The device of claim9 wherein: said sleeve and control features are formed as a unitarymember.
 11. The device of claim 1 further including: a thrust featuredisposed along the control member, spaced apart proximally from thecontrol feature, and positioned to allow limited proximal travel of thedelivery member and prosthesis relative to the control member when inthe delivery position with the prosthesis so contained, and to engagethe proximal end of the prosthesis responsive to said limited proximaltravel and thereby prevent further proximal travel of the prosthesisrelative to the control member.
 12. The device of claim 11 wherein: thelinking structure has an axial dimension along a portion thereofdisposed between the thrust feature and the control feature when theprosthesis is so contained, and an axial spacing between the thrustfeature and the control feature is selected to determine a range, foraxial travel of the prosthesis relative to the control member, of 3.3 to6.7 times said axial dimension.
 13. The device of claim 12 wherein: saidrange for axial travel is at least about 0.7 mm and at most about 1.7mm.
 14. The device of claim 1 wherein: the linking structure defines atleast one linking aperture, and the control feature is disposed toextend into the linking aperture.
 15. The device of claim 14 wherein:the linking structure defines a plurality of linking apertures near theproximal end of the prosthesis; the control feature comprises aplurality of the control features, each adapted to extend into adifferent one of the linking apertures.
 16. The device of claim 14wherein: the control feature extends through the linking aperture, to alocation radially outwardly of the linking structure.
 17. The device ofclaim 5 wherein: the control features comprise hooks.
 18. The device ofclaim 5 wherein: the control features comprise pins.
 19. The device ofclaim 5 wherein: the control features comprise elongate axially extendedfins.
 20. The device of claim 5 wherein: the control features haveradially outward ends cooperating to define a control feature outerdiameter less than an inside diameter of the distal wall segment. 21.The device of claim 20 wherein: a radial spacing between the radiallyoutward ends of the control features and the distal wall segment of thedelivery member is less than half of a radial thickness dimension of theprosthesis.
 22. The device of claim 1 wherein: a radial self-expansionof the prosthesis upon its release from the delivery member carries thelinking structure radially outward beyond the control feature, thus todisengage the prosthesis from the control member.
 23. The device ofclaim 1 wherein: the linking structure comprises an elongate linkingstrand formed into a loop to provide a linking aperture.
 24. The deviceof claim 23 wherein: the control feature comprises a first componentcontained within the loop, and a second component disposed outside ofthe loop, spaced apart from the first component, and cooperating withthe first component to form a first recess to releasably contain a firstsegment of said linking strand.
 25. The device of claim 24 wherein: saidcontrol feature further includes a third component disposed outside theloop on a side of the loop opposite the second component, and spacedapart from the first component to define a second recess for releasablycontaining a second segment of said strand.
 26. The device of claim 25wherein: said first and second recesses extend substantially in theaxial direction.
 27. The device of claim 23 wherein: the linkingstructure comprises a plurality of loops, and the control featurecomprises a plurality of the control features, wherein each of thecontrol features is associated with a different one of the loops. 28.The device of claim 23 wherein: the prosthesis is an open frame tubularstructure formed of a plurality of elongate strands, including saidlinking strand.
 29. A prosthesis delivery and deployment device,including: an elongate prosthesis delivery member having a distal wallsegment adapted to contain a radially self-expanding prosthesis in areduced-radius delivery state against an internal restoring force; anelongate control member mounted for axial travel relative to thedelivery member, toward and away from a delivery position in which adistal end region of the control member extends along the distal wallsegment of the delivery member; and a prosthesis anchor mounted to thedistal end region and comprising at least one elongate axially directedcontrol feature extending radially outwardly from the control member andthereby positioned to effect a releasable engagement with a proximal-endlinking structure of a radially self-expanding prosthesis when in thedelivery position and with the prosthesis so contained; wherein theanchor, when in said engagement with the linking structure, is operableto anchor the prosthesis against distal travel relative to the controlmember.
 30. The device of claim 29 further including; a self-expandingprosthesis including a proximally disposed linking structure andcontained by said distal wall segment in the reduced-radius deliverystate.
 31. The device of claim 30 further including: a thrust featuremounted to the control member proximally of the anchor and operable,through proximal travel of the delivery member relative to the controlmember with the prosthesis so contained, to establish surface contactwith the linking structure to anchor the prosthesis against furtherproximal movement relative to the control member.
 32. The device ofclaim 31 wherein: the linking structure has an axial dimension along aportion thereof disposed between the control feature and the thrustfeature when the prosthesis is so contained; and an axial spacingbetween the control feature and the thrust feature is selected todetermine a range, for axial travel of the prosthesis relative to thecontrol member, of 3.3 to 6.7 times the axial dimension.
 33. The deviceof claim 32 wherein: said range is at least about 0.7 mm and at mostabout 1.7 mm.
 34. The device of claim 30 wherein: the linking structureincludes an elongate linking strand formed into an elongate axiallydirected loop, and the control feature when so positioned extends intothe loop.
 35. The device of claim 34 wherein: the anchor includes ananchoring body with a recess directed inwardly from an outside surfaceof the anchoring body and adapted to receive the loop, and the controlfeature is disposed in the recess and extends radially outward throughthe loop when the loop is in the recess; and said recess includes firstand a second recess segments on opposite sides of the control feature.36. The device of claim 35 wherein: the elongate linking strand includesopposed, substantially axially directed parallel first and second loopsegments, and the first and second recess segments extend axially tocontain the first and second loop segments, respectively.
 37. The deviceof claim 35 wherein: an inside diameter of the distal wall segment islarger than an outside diameter of the anchoring body, by an amount lessthan a radial thickness dimension of the loop.
 38. The device of claim37 wherein: said recess is directed inwardly a distance greater thansaid radial thickness dimension of the loop.
 39. The device of claim 29wherein: the anchor comprises a plurality of the elongate radiallydirected control features positioned to effect said releasableengagement with the linking structure.
 40. The device of claim 39wherein: the proximal-end linking structure comprises a plurality ofelongate axially directed loops, each associated with a different one ofthe control features.
 41. The device of claim 29 wherein: the distal endregion is surrounded by the prosthesis when in said delivery position.42. The device of claim 29 wherein: the delivery member comprises anelongate outer catheter having a lumen running substantially the entirelength of the outer catheter.
 43. The device of claim 42 wherein: thecontrol member comprises an elongate inner catheter disposed in saidlumen, with a proximal region of the inner catheter extending proximallybeyond a proximal end of the outer catheter to facilitate use of theproximal region to control a position of the distal region relative tothe outer catheter.
 44. The device of claim 29 wherein: the anchorincludes a cylindrical anchoring body with a centrally located axialopening therethrough adapted to receive the control member andfacilitate a mounting of the anchor in surrounding relation to thecontrol member.
 45. The device of claim 30 wherein: the proximal-endlinking structure comprises a plurality of elongate axially directedloops angularly spaced apart from one another about the prosthesis; andsaid anchor comprises a plurality of the elongate axially directedcontrol features angularly spaced apart from one another about thecontrol member, and each of the control features is positioned toreleasably engage a different one of the loops.
 46. The device of claim45 wherein: the number of control features equals the number of loops.47. The device of claim 45 wherein: the number of loops is an integralmultiple of the number of control features.
 48. A prosthesis anchoringdevice adapted for fixation to a prosthesis deployment member, theanchoring device including: a generally cylindrical anchoring sleevehaving a central opening extending axially therethrough to facilitate aslideable installation of the anchoring sleeve onto an elongateprosthesis deployment member for fixation along a distal end region ofthe deployment member; and a control feature extended radially outwardlyfrom the anchoring sleeve and adapted to extend radially into aproximal-end linking structure of a radially self-expanding prosthesiswhen the prosthesis is maintained in a reduced-radius state against aninternal restoring force and selectively axially aligned with saiddistal end region; whereby the control feature, with the anchoringsleeve fixed to a deployment member and when so extending into aproximal-end linking structure of a radially self-expanding prosthesisso maintained and aligned, is adapted to engage the linking structure toprevent any substantial distal movement of the prosthesis relative tothe deployment member.
 49. The device of claim 48 wherein: the controlfeature is elongate, directed axially, and adapted to extend into aproximal-end linking structure in the form of an elongate, axiallyextended loop.
 50. The device of claim 49 wherein: the control feature,when surrounded by the loop, prevents any substantial axial movement ofthe loop relative to the anchoring body.
 51. The device of claim 48wherein: the anchoring sleeve and the control feature are formed as aunitary member.
 52. The device of claim 48 including: a plurality of thecontrol features angularly spaced apart from one another about theanchoring body.
 53. The device of claim 48 wherein: the anchoring bodyincludes a recess containing the control feature, adapted to receive aprosthesis proximal-end linking structure, and having a depth in theradial direction larger than a radial thickness of the linkingstructure.
 54. The device of claim 53 wherein: the recess includes firstand second recess segments disposed on opposite sides of the controlfeature for containing opposite sides of a prosthesis proximal-endlinking structure in the form of a loop disposed in the recess.
 55. Aprocess for loading a radially self-expanding prosthesis for subsequentdeployment in a body lumen, including: positioning a radiallyself-expanding prosthesis along and in surrounding relation to a distalend region of an elongate prosthesis control member with a proximal endlinking structure of the prosthesis disposed near axially spaced apartfirst and second features that extend radially outwardly from thecontrol member; with the prosthesis so positioned, radially contractingthe prosthesis to a reduced-radius delivery state against an internalelastic restoring force to move the linking structure into a deliveryposition between the first and second features whereby the first andsecond features cooperate to limit axial travel of the prosthesisrelative to the control member to a predetermined range so long as theprosthesis is maintained in the delivery state; and selecting an axialdimension of the linking structure with respect to an axial spacingbetween the first and second features whereby the predetermined range isat least twice the axial dimension of the linking structure.
 56. Theprocess of claim 55 wherein: radially contracting the prosthesiscomprises progressively advancing a prosthesis delivery member over theprosthesis to contain the prosthesis in the delivery state within alumen of the delivery member.